1. Field of the Invention
The present invention relates to a powder transport apparatus that transports powder such as toner from a powder container to a transport destination located lower than the powder container via a powder transport tube, and to an image forming apparatus including the powder transport apparatus.
2. Description of the Related Art
Conventionally, image forming apparatuses such as copying machines, facsimile machines, and printing machines are known that use a toner feeding apparatus. The toner feeding apparatus includes, for example, toner providing means for providing toner from a toner container and a feeding tube connecting a developing part and the toner container. The developing part develops a latent image carried on a latent image carrier such as a photo conductor into a toner image. The toner providing means are operated in accordance with need so as to provide toner contained in the toner container into the feeding tube, and the toner is directly fed into the developing part via the feeding tube.
Assuming that the toner container is arranged at a position lower than the developing part in an image forming apparatus using such a toner feeding apparatus, it is necessary to feed the toner provided from the toner container into the feeding tube to flow upward to the developing part against gravity. Hence, feeding efficiency may be decreased, or the feeding tube is likely to be blocked by the toner.
Accordingly, generally, the toner container is arranged at a position higher than the developing part so as to feed the toner in the gravity direction. Toner feeding apparatuses that perform feeding in the gravity direction in the aforementioned manner include, for example, a toner feeding apparatus described in Japanese Laid-Open Patent Application No. 8-30097. In the toner feeding apparatus, toner provided from a toner box, which is the toner container, into the feeding tube is fed into the developing part by making the toner fall by its own weight.
In the toner feeding apparatus, however, there is a probability that the toner will flow into the developing part at a blast (sudden rapid rate) when the toner disposed on an inside wall of the feeding tube reaches a certain large amount (builds up). When the toner flows into the developing part at a blast as mentioned above, in a binary developer method that uses a binary developer including toner and a magnetic carrier, for example, it is difficult to control the toner concentration of the binary developer. Additionally, in a single-component developing method that uses only toner without using a magnetic carrier, for example, the ratio of the toner that is not sufficiently friction-charged within the developing part rapidly increases, and so-called scumming, which causes the toner to adhere to a non-image portion of a latent image carrier, is likely to occur. It is possible to make the length of the feeding tube short by arranging the toner box and the developing part close to each other so as to prevent the toner from being built up within the feeding tube. However, flexibility in layout in the image forming apparatus is decreased due to the restriction of such a close arrangement of the toner box and the developing part.
Therefore, it is conceivable to provide in the feeding pipe means for applying a feeding force to the toner, for example, a coil. By applying the feeding force to the toner, it is possible to prevent the toner from accumulating within the feeding tube and prevent the accumulated toner from flowing into the developing part at a blast.
In a case where such a structure is adopted, however, the cross-sectional area of the coil is small with respect to that of the space inside the feeding tube. Thus, in the cross-sectional area of the feeding tube, those portions that are not filled with the cross-sectional area of the coil serve as spaces that allow the toner to pass therethrough. Hence, when a large amount of the toner is provided at a blast from the toner container, the toner flows through the spaces, i.e., the toner flows into the developing part irrespective of rotation of the coil. Accordingly, there is a possibility that replenishment control of the toner with respect to the developing part may be unstable.
A description is given above regarding the problems that may occur in the toner feeding apparatuses that feed toners as powders. However, also in other powder feeding apparatuses that feed powders that are different from toners, there is a possibility that some problems may occur when replenishment control of powders flowing from inside the feeding tube to a feeding destination becomes unstable.